Lock 2.0.x to pre-Symfony AI Platform until it contains Embeddings endpoints
## Summary
Per https://git.drupalcode.org/project/ai_search/-/work_items/3584015#note_1075667 AI Core 2.0.x has introduced breaking changes that stop its support for Embeddings temporarily because of partial completion of Symfony AI integration. AI Core after commit ID `bfa34269` therefore no longer supports AI Search until that above issue is resolved
## Steps to reproduce
View AI Search pipelines
## Expected result
Tests pass
## Actual result
Tests fail
issue